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Biomedical subjects

J D Duncan

Publications and source records attributed to J D Duncan.

33 records · Page 2Linked to original sources
PubMed1984

Pulmonary blastomycosis: radiologic manifestations.

Blastomycosis, an airborne fungal disease with the lung the portal of entry, is endemic to the central and south central areas of the United States. The disease occurs in patients who range from asymptomatic to those with symptoms of acute pneumonia. Retrospective review of 27 cases from our institution revealed four well-defined radiographic patterns including air-space disease, nodular masses, interstitial disease, and cavitation. Some patients with air-space disease have symptoms of an acute pneumonia; more commonly they have no pulmonary symptoms. Air-space disease was the most frequent radiographic pattern in chronic blastomycosis with proved nonpulmonary disease; therefore, it cannot be regarded as indicative of early or acute blastomycosis. There was no relationship between the radiographic pattern and distribution, pulmonary symptomatology, or clinical stage of the disease. Our material does not support the previously suggested association of lower lobe air-space disease with early disease and upper lobe involvement with the chronic and often disseminated form. A more precise understanding of the variety of radiographic patterns and the spectrum of clinical presentations will facilitate diagnosis of pulmonary blastomycosis.

Adolescent↗
PubMed1982

The casting accuracy of nickel--chromium alloys for fixed prostheses.

The casting accuracy of four nickel--chromium alloys (Ultratek, Omega, Microbond N/P2, and Nobil-Ceram) was compared to that of a precious alloy, Jelenko "O". The experiment consisted of fabricating and fitting cast copings to a cobalt--chromium test preparation of a maxillary central incisor and measuring the marginal discrepancy in eight selected points. The experiment indicated that Jelenko "O" had the greatest casting accuracy, followed successively by Ultratek, Nobil-Ceram, Microbond N/P2, and Omega. Statistical analysis of the data revealed no significant difference between Jelenko "O" and Ultratek alloys in fit of five of eight test points, but Jelenko "O" was significantly better in fit than Nobil-Ceram, Microbond N/P2, and Omega alloys. The following conclusions may be drawn from this experiment: 1. The nickel--chromium alloys tested did not cast as consistently or as accurately as precious alloy Jelenko "O". 2. The casting accuracy may be related to the amount of casting shrinkage that occurs in each alloy type, and further research is necessary to determine if expansion compensation of the selected phosphate-bonded investment recommended by the alloy manufacturers is adequate for the casting shrinkage of the test alloys. 3. Alloy composition and technique parameters may also influence the accuracy of the casting, but further research is necessary to determine their singular effects.

Chemical Phenomena↗
PubMed1982

N-oxidation of phentermine to N-hydroxyphentermine by a reconstituted cytochrome P-450 oxidase system from rabbit liver.

Previous studies in our laboratory have indicated that the cytochrome P-450 system is involved in the oxidation of phentermine (2-methyl-1-phenyl-2-aminopropane) to N-hydroxyphentermine by liver microsomal preparations. In the present study, a reconstituted system which consisted of cytochrome P-450 and NADPH cytochrome P-450 reductase purified from liver microsomes of phenobarbital-induced rabbits was found to oxidize phentermine to N-hydroxyphentermine. The reaction was NADPH-dependent and required the presence of both the cytochrome P-450 and reductase preparations. N-Hydroxyphentermine was formed 3 times more rapidly in incubation mixtures which contained dilauroyl phosphatidylcholine than in those without added phospholipid. The reaction was inhibited several-fold by octylamine. It is concluded that the cytochrome P-450 system is able to catalyze the oxidation of phentermine to N-hydroxyphentermine.

Animals↗
PubMed1981

Properties of Kaurene Synthetase from Marah macrocarpus Endosperm: Evidence for the Participation of Separate but Interacting Enzymes.

Ent-kaurene is synthesized from geranylgeranyl pyrophosphate in a two step sequence catalyzed by kaurene synthetase; the first step (A activity) involves the conversion of geranylgeranyl pyrophosphate into the intermediate ent-trans labda-8(17), 13-dien-15-yl pyrophosphate (copalyl pyrophosphate) which is further cyclized to ent-kaurene in the second step (B activity). The resolution of enzyme fractions which catalyze each step independent of the other has been accomplished for the first time by means of QAE Sephadex A-50 chromatography and polyacrylamide gel electrophoresis of kaurene synthetase preparations from endosperm tissue of immature seed of Marah macrocarpus. Molecular weights for the A and B enzymes were each estimated as approximately 82,000 by means of gel filtration chromatography and sedimentation velocity determinations.Experiments in which [(14)C]geranylgeranyl pyrophosphate and [(3)H]copalyl pyrophosphate were incubated simultaneously with kaurene synthetase preparations demonstrated that copalyl pyrophosphate derived from [(14)C]geranylgeranyl pyrophosphate is more readily converted to kaurene than is exogenously added [(3)H]copalyl pyrophosphate. This implies that copalyl pyrophosphate derived from the catalytic site of the A enzyme is preferentially channelled to the B enzyme catalytic site for conversion to ent-kaurene, rather than freely equilibrating with a pool of copalyl pyrophosphate in the medium. Experiments in which the rates of the overall AB and independent B activities of kaurene synthetase preparations were measured as a function of total protein concentration further suggest that overall AB activity is catalyzed by an AB enzyme complex which is in equilibrium with free A and B enzymes. A model is proposed for M. macrocarpus kaurene synthetase in which separate but interacting A and B enzymes must associate for the efficient production of ent-kaurene from geranylgeranyl pyrophosphate.

Journal Article↗
PubMed1977

Familial renal disease in Norwegian Elkhound dogs: morphologic examinations.

Periglomerular and interstitial fibrosis were the earliest renal lesions in 21 Norwegian Elkhound (NE) dogs with familial renal disease. Histopathologic study did not reveal the cause of the disease, and light microscopy did not show renal lesions different from nonfamilial renal lesions commonly observed in dogs. Histopathologic evaluation was reliable for detecting disease in NE dogs prior to onset of isosthenuria and azotemia. Results of glomerular counts, determining kidney size, and dissection of the nephron indicated that nephron numbers and size were adequate early in the disease, but that numbers decreased as the disease progressed. Electron microscopic and immunofluorescent studies were not suggestive of an immune basis of the renal disease, nor did histopathologic or angiographic studies indicate primary vascular lesions. Nephron dissections revealed sacculations in distal tubules and collecting ducts of affected NE dogs. Renal disease did not develop in mongrel pups given injections of an homogenate or renal tissue from an affected NE dogs.

Animals↗
PubMedDate not supplied

Fabricating a gold occlusal platform on a removable partial denture to help prevent extrusion of mandibular incisors.

A clinical procedure is presented in which a maxillary removable partial denture replacing anterior teeth was fabricated with a cast gold anterior occlusal platform. This treatment is indicated to correct abrasion caused by extruded mandibular anterior teeth on the maxillary removable partial denture. The advantages compared to prosthetic teeth supported by an acrylic resin base or metal-backed facings are discussed. This technique allows for development of optimal esthetics, strength, and durability while preventing further extrusion and excessive wear of the teeth occluding against prosthesis.

Denture Design↗
PubMedDate not supplied

Benign fibrous histiocytoma: a rare endobronchial neoplasm.

Fibrous histiocytomas are rarely found within the lung and have presented as a mass within a major airway only twice previously. This is the third reported case of such a tumor visualized roentgenographically in an airway on the frontal chest film of a patient presenting with recurrent pneumonia.

Adult↗
PubMedDate not supplied

Effects of alpha-carbon substituents on the N-demethylation of N-methyl-2-phenethylamines by rat liver microsomes.

The effects of methyl, ethyl, isopropyl, isobutyl, and benzyl substituents at the alpha-carbon of N-methyl-2-phenethylamine on the kinetics of its N-demethylation in liver microsomes from both control and phenobarbital pretreated rats were studied. In control microsomes, the kinetic studies indicated that more than one enzyme was active for N-demethylation of N-methyl-alpha-methylphenethylamine (methamphetamine) while the other N-methyl-2-phenethylamines appeared to be demethylated by a single enzyme. In microsomes from phenobarbital pretreated animals, there appeared to be more than one enzyme system which was active for N-demethylation of all compounds except N-methyl-alpha-benzylphenethylamine. One of these had a much higher affinity for alpha-ethyl, isopropyl, and isobutyl N-methylphenethylamines while another exhibited affinities for substrates similar to the constitutive enzyme in control microsomes. A correlation was observed between the octanol-buffer or heptane-buffer distribution ratios of the compounds and the negative logarithm of the Michaelis constant (pKm) for the enzyme in control microsomes and for each of the enzyme systems in microsomes from phenobarbital-pretreated animals. Therefore, it is indicated that the concentration of a substrate at the active site of these microsomal enzymes is a function of its lipid solubility.

Animals↗